A is the baseline amount. With price ratio K, fixed-money purchasing power is A/K at start-period prices; the nominal amount needed for the same basket is A×K. These are inverse questions.
Two price questions, two dollar bases
Inflation comparisons answer two inverse questions. If a starting basket costs $1,000 and the selected price index rises by 10%, buying that basket at the ending period requires $1,100. Holding a fixed $1,000 instead leaves purchasing power of about $909.09 at starting-period prices. The difference does not mean that the account paid a cash fee or that both answers should be added together. Each describes the same price ratio from a different dollar basis.
The calculator keeps both answers visible and identifies the selected question in the headline. Historical mode obtains its ratio from positive official observations in one named CPI-U series. Future mode compounds a hypothetical annual assumption. Same-period comparisons have a ratio of one; reversing historical endpoints takes the reciprocal. Deflation can therefore increase fixed-dollar purchasing power while reducing the nominal amount needed for the original basket. Select a plotted period or open the table to inspect its exact index, ratio and two values, then use CSV for the unrounded calculation data.
Published observations and household assumptions
The historical snapshot uses BLS all-items CPI-U for the U.S. city average, not seasonally adjusted, with the 1982–84 index base of 100. An annual average and a monthly observation summarize different periods. Choose the convention before interpreting the ratio. The stored monthly series retains October 2025 as unavailable; it does not copy September, interpolate November or invent a complete current-year average. The official 2025 annual average separately follows BLS methodology using 11 published months.
CPI describes a population basket and cannot establish one household's actual price change. The optional projection basket instead accepts user-assumed category rates and spending weights. For example, weights of 25% at 10% inflation and 75% at −2% imply a weighted annual assumption of 1%. Halving both weights leaves that normalized assumption unchanged. Selecting this option replaces the manual future inflation rate without altering official observations or the independent investment-return assumption. The example item prices below the chart are also editable starting-price assumptions, not historical retail quotes or a claim about every household.
Cash-flow timing and comparisons
Price observations and investment returns have different timing. The retained S&P 500 illustration uses sourced calendar-year total returns, including dividends. A forward annual path compounds the ending calendar years; a reverse path applies reciprocal factors. Annual-average CPI does not measure precisely those same calendar-end dates, so the comparison is an illustration rather than an exact historical investment real return. Monthly CPI does not create monthly market returns: the market and related tax series remain unavailable in that view.
Future investment, savings-account, bond and gold paths use disclosed hypothetical rates. The optional tax illustration reduces positive annual investment gains and provides no automatic tax credit for losses. Its reverse historical factors are not a reconstruction of actual tax payments. The exact Fisher relation compares compatible annual return and inflation factors rather than simply subtracting rates. A captured baseline retains its own periods and source version; if its historical/future mode or observation convention differs from the current scenario, the page lists both contexts without presenting them as a matched comparison or a probability.
Planning in Today's Dollars
The goal planner first expresses a target stated at today's prices as the nominal amount needed at the chosen future horizon. It then calculates either a starting lump sum or equal end-month deposits using a separately entered effective annual investment-return assumption. The calculation excludes contributions at time zero, and its monthly factor is consistent with the selected annual return. Zero and negative assumed returns remain meaningful mathematical cases; unavailable arithmetic is reported instead of a fabricated payment.
The wage illustration applies one annual raise and one inflation assumption for ten years. Its real change uses the exact ratio of the two growth factors. The retirement panel only translates a nominal future balance into starting-price dollars and shows a hypothetical 4% annual amount; it does not model retirement cash flows or establish a safe withdrawal rate. Review each panel's horizon and units before comparing values. Ordinary edits neither write financial URL parameters nor silently save a new device draft. Remember and reviewed Share are explicit separate choices; Reset clears only this calculator's saved state.